The use of optical signals to represent data and other information in communication and data processing applications has become increasingly popular. The increased popularity is due in large part to the significantly higher bit rates allowed by the higher frequencies of the carrier signals, over conventional electrical conductor or wireless techniques. The switching or modulation of information from a source to its destination is a critical function in any communication or data processing system. Many optical systems, however, have experienced difficulty with the switching or modulation of the optical signals, and in particular have encountered difficulties with optical transmissions due to the lossy nature of many conventional optical interfaces.
A number of optical switches and modulators have been developed or proposed which utilize the magneto-optic or electro-optic effect to vary the optical properties, such as the refractive index, of an optical material, upon the application of the appropriate magnetic or electric field. For a discussion of conventional optical switching and modulation devices based on the magneto-optic or electro-optic effect, see, for example, U.S. Pat. No. 4,211,467 to Cross et al. and U.S. Pat. No. 4,820,009 to Thaniyavarn.
Glass waveguides are often utilized in optical devices because they exhibit lower loss and stable optical properties, and are easier to couple to optical fibers. Unlike semiconductor and electro-optic materials, however, the optical properties of glass waveguides are often difficult to control. A number of optical devices have been developed or proposed which utilize a stress applied to a glass fiber or waveguide to alter the index of refraction of the glass. These optical devices, however, do not allow a variable stress to be applied to the waveguide. Thus, these devices do not allow a continuous range of optical intensities to be provided at the output of the optical device.
For example, one system, described in Marayuki Okuno et al., "Birefringence Control of Silica Waveguides on Si and Its Application to a Polarization-Beam Splitter/Switch", Journal of Lightwave Technology, Vol. 12, No. 4, pp. 625-33 (April, 1994), has been proposed which applies a permanent fixed stress during the fabrication process to one or more glass waveguides in an integrated optical device to establish desired refractive indices and birefringence. Thereafter, during operation, the thermo-optic effect is utilized to alter the optical properties of the waveguides to achieve switching or modulation.
While the Okuno system provides an effective basis for switching an optical signal from one path to another, or for modulating an optical signal between an on and off state, the Okuno system requires the continuous application of power to heat regions of the optical device. In addition, the applied heat may not be localized to a desired region of the waveguides in the integrated optical device, which is of particular concern, for example, where the two waveguides come close together in the coupling region of the integrated optical device.
U.S. Pat. No. 5,095,515, to Seaver, shows an optical switch for altering the path of an optical beam. The optical switch disclosed in Seaver is embodied as an unpatterned planar waveguide and utilizes an applied stress to alter the index of refraction of the planar waveguide material and thereby deflect the optical beam from an unstressed optical beam path to a stressed optical beam path. The stress may be applied to the planar waveguide by means of a magnetostrictive, electrostrictive or photostrictive material. While the Seaver system provides an effective mechanism for utilizing an applied stress to vary the index of refraction of a planar waveguide, the Seaver system does not confine the optical beam path to a particular defined path or channel through the device. In addition, planar waveguides are typically characterized by a lossy interface between the waveguide and an optical fiber.
As is apparent from the above discussion, a need exists for an improved integrated optical switching or modulation device. In addition, a need exists for an integrated optical switching or modulation device that allows a variable stress to be applied to a waveguide in order to alter the optical properties of the waveguide in a controlled and variable manner. A further need exists for integrated optical devices capable of switching or modulating an optical signal among channel waveguides without regard to the wavelength or polarization of the signal.